Various types of biometric systems are used more and more in order to provide for increased security and/or enhanced user convenience.
In particular, fingerprint sensing systems have been adopted in, for example, consumer electronic devices, thanks to their small form factor, high performance, and user acceptance.
To save cost and valuable surface space, there is an effort towards smaller and smaller fingerprint sensors, which may be substantially smaller than the user's fingerprint.
One way of achieving satisfactory biometric performance with a small fingerprint sensor is to provide a so-called swipe sensor or strip sensor. By instructing the user to swipe his finger across the sensor surface and capturing image slices during the swiping motion sufficient fingerprint information can be collected.
For some applications, however, swiping the finger across the sensor may not be considered to be sufficiently intuitive and simple to the user.
For such and other applications, fingerprint sensing systems employing small sensors for stationary finger placement have been proposed. In such fingerprint sensing systems, the user may be authenticated against a stored template based on a single partial fingerprint image from the sensor.
For achieving the desired satisfactory biometric performance when authenticating based on a single partial fingerprint image from a small fingerprint sensor, it may be necessary that the stored template corresponds to a considerably larger portion of the user's fingerprint than the partial fingerprint image captured in connection with an authentication attempt.
One way of achieving such a larger template is to enroll users on a larger fingerprint sensor. This approach is, however, not suitable for many applications where enrollment and authentication should be carried out using the same electronic device, such as a mobile communication device.
It has therefore been proposed to require the user to place his/her finger on the small fingerprint sensor several times during enrolment and then combine data from several partial images to form the template. Depending on, for example, the variation in finger placement and the size of the fingerprint (the size of the finger), it may be difficult to determine if or when sufficient fingerprint data has been acquired based on a given number of finger placements. Alternatively, to ensure that sufficient fingerprint data is always acquired, the enrolment procedure may require a very large number of finger placements upon enrolment. This approach, however, would lead to a time-consuming enrolment procedure, which may result in the user deciding not to use the fingerprint-based authentication system at all.
In view of this, US2013/0259330 discloses a method and system for continuously updating and expanding an enrolled template using later acquired partial fingerprint images that match with the stored template.
However, there appears to still be room for improvement. In particular, it would be desirable to provide for a faster expansion of the enrolled template.